Method for identification of low/non-addictive opioid analgesics and the use of said analgesics for treatment of opioid addiction

ABSTRACT

The present invention relates to a method of using a bioassay consisting of an electrophysiological method and a cell culture system of dorsal-root ganglion (DRG) neurons to screen and identify opioids with a high potential for use as &#34;low- or non-addictive&#34; analgesics. Another aspect of the invention relates to a specific group of opioid alkaloids and analogues thereof identified by the bioassay of the invention for the unique ability to activate only inhibitory, but not excitatory, opioid receptor function, for use as low- or non-addictive analgesics. Another aspect of the invention relates to the specific use of etorphine or dihydroetorphine of the opioid alkaloid family as low- or non-addictive analgesics and for the treatment of opioid addiction.

This invention was made in part with Chinese Government support underresearch grants CO3020801 awarded by National Foundation of Sciences ofChina, 85-922-02-22 awarded by Foundation of National Committee ofScience and Technology of China; and 9009120 awarded by AMMS ResearchGrant; and support from United Biomedical Inc.'s general research fund.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 08/088,503filed Jul. 7, 1993, now abandoned, which is a continuation-in-partapplication of application Ser. No. 977,332 filed Nov. 17, 1992, nowabandoned, which is a continuation-in-part application of Ser. No.947,690 filed Sep. 21, 1992, abandoned.

FIELD OF THE INVENTION

The present invention relates to a specific group of opioid agonists foruse as low/non-addictive analgesics and for treatment of opioidaddiction. More particularly, the present invention is directed toetorphine, dihydroetorphine, and other opioid and analogues thereof thatare effective as low/non-addictive analgesics and for the treatment ofopioid addiction. In addition, this invention provides a bioassay methodto screen and identify such compounds with the ability to selectivelyactivate inhibitory but not excitatory opioid receptor-mediatedfunctions.

BACKGROUND OF THE INVENTION

Since the introduction of morphine to the clinic as a pain reliever,clinicians have been troubled with the problem of drug addiction. Formore than a century, chemists, pharmacologists, and clinicians havestrived to find an ideal analgesic with high potency, yet lowaddictivity. A series of opioids such as meperidine, methadone, andfentanyl were subsequently developed.

However, none of these drugs exert sustained analgesic effects inpatients without developing addiction. In Western countries, methadonesubstitution has been employed for the treatment of drug abuse for sometime. Unfortunately, methadone induces significant psychological andphysical dependencies. Consequently, patients undergoing such treatmentusually convert to methadone dependence during withdrawal from chronicuse of morphine, heroin or other opioids (Jaffe, 1990). Therefore theneed remains to develop better methods based upon insights into themolecular and cellular mechanisms underlying opioid addiction fortreating drug abuse and particularly a means to identify compounds foruse as low- or non-addictive analgesics and for suppression of opioidwithdrawal symptoms.

SUMMARY OF THE INVENTION

The present invention is directed to an in vitro screening method foridentifying a low- or non-addictive opioid analgesic by screeningopioids to identify a compound which is capable of evoking an inhibitoryeffect but not an excitatory effect on opioid receptor-mediatedfunctions of sensory neurons in a dose-dependent manner over theconcentration range of from about femtomolar (fM) to about micromolar(μM). In particular, such opioid compounds are identified by recordingthe action potential duration (APD) of a sensory neuron elicited by thecompound in a cell culture screening assay and selecting those opioidcompounds which shorten the APD but do not prolong the APD relative to acontrol APD when the compounds are assayed in the concentration range ofabout fM to about μM. Opioid compounds with these characteristics arethereby identified as low- or non-addictive opioid analgesics of theinvention. Preferably, the cell culture screening assay comprisesexposing a dorsal-root ganglion (DRG) neuron to the candidate compound,typically by bath perfusion, applying a brief intracellular depolarizingcurrent to said DRG neuron, and recording opioid-induced alteration inthe APD of the DRG neuron using standard electrophysiologicaltechniques.

Another aspect of the invention, thus, provides low- or non-addictiveanalgesics, particularly as identified by the method of the presentinvention, which are capable of evoking the inhibitory but not theexcitatory effects of opioid receptor-mediated functions, particularlyon sensory neutrons, in a dose-dependent manner in concentrationsranging from about fM to about μM. In a preferred embodiment theseopioids include etorphine or dihydroetorphine. Pharmaceuticalcompositions containing the subject low- or non-addictive opioids, orpharmaceutically acceptable salts thereof, together withpharmaceutically acceptable carriers are also provided.

Yet another aspect of this invention provides a method of treatingopioid addiction by administering an effective amount of a non-addictiveopioid analgesic, or an analog thereof, to a patient for a timesufficient to relieve or suppress withdrawal symptoms that occur whenthe addictive opioid is withheld from the addict. After the initialadministration of the non-addictive opioid analgesic for a period topermit alleviation of the withdrawal symptoms, the dose of thenon-addictive opioid analgesic is gradually decreased from the originaldose to zero over time sufficient to fully wean said patient from saidanalgesic without untoward side effects. Typically the initialadministration of the non-addictive opioid analgesic lasts for about 1to about 5 days and the weaning period lasts from about 1 to about 7days, so that a patient can be withdrawn from opioid addiction within anoverall about 2 to 12 day period. In a preferred embodiment thenon-addictive opioid analgesic is etorphine or dihydroetorphineinitially administered at a dose of from about 10 μg to about 1000 μgper day. Such dosages are usually administered sublingually,intramuscularly or intravenously, preferably by intravenous dripping,depending on the severity of the withdrawal symptoms in the patient.Even more preferably, opioid addiction is treated by administering about40 to about 500 μg of dihydroetorphine per day to a patient for aboutone to about three days, administering a decreasing amount ofdihydroetorphine for the following about four to about seven days sothat no further dihydroetorphine is necessary by about 10 days after thefirst administration of dihydroetorphine.

A further aspect of the invention provides a method of treating opioidaddiction by administering an effective amount of a non-addictive opioidanalgesic, to a patient for a time sufficient for immediate relief orsuppression of withdrawal symptoms due to said opioid addiction;administering an effective amount of a longer-acting replacement opioidfor a time sufficient to maintain the relief or suppression ofwithdrawal symptoms, followed by administering a decreasing dose of thenon-addictive opioid analgesic for a time sufficient to wean saidpatient from said opioid analgesic without untoward side effects.Typically the initial administration of the non-addictive opioidanalgesic lasts for about 1 to about 3 days, the administration of thereplacement opioid lasts for about 1 to about 3 days, and the return tothe non-addictive opioid analgesic with its concomitant weaning periodlasts from about 1 to about 8 days, so that a patient can be withdrawnfrom opioid addiction within an overall 3 to 14 day period.

In a preferred embodiment the non-addictive opioid analgesic isetorphine or dihydroetorphine initially administered at a dose of fromabout 10 μg to about 1000 μg per day. Such dosages are usuallyadministered sublingually, intramuscularly or by intravenous drippingdepending on the severity of the withdrawal symptoms in the patient.Preferably the replacement opioid is methadone administered per os at adose of about 5-100 mg/day.

A still further aspect of the invention provides a method of treatingacute or chronic pain with a low- or non-addictive opioid analgesic. Inparticular, dihydroetorphine hydrochloride (DHE) is administered to apatient for a time and in an amount effective to relieve or suppresspain without resultant addiction. Treatment for acute pain is typicallyaccomplished by administration of about 20-60 μg DHE sublingually, up toabout 180 μg per day for the duration of the pain, and typically nolonger than 1 week. Treatment for chronic pain is typically accomplishedby administration of about 20-100 μg DHE sublingually, up to 400 μg perday, and such administration can last several months. In rare instancestreatment of chronic pain can result in mild addiction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates that acute application of pM-μM concentrations ofetorphine to a naive DRG neuron elicits inhibitory shortening of theAPD. 1: Action potential (AP) generated by a DRG neuron in Hank'sbalanced salt solution containing 5 mM Ca²⁺ and 5 mM Ba²⁺ (BSS). APresponse in this record (and in all records below) was evoked by a brief(2 msec) intracellular depolarizing current pulse. 2-5: The APD isprogressively shortened by bath perfusion of 1 fM, 1 pM, 1 nM and 1 μMetorphine, respectively. 6: After washout of etorphine, the APDrecovers.

FIG. 2 shows the dose-response relationship of etorphine, DHE anddynorphin (1-13) (Dyn 1-13) effects on the APD of DRG neurons. Etorphineand DHE elicited a dose-dependent shortening of the APD (n=11 and 13,respectively). In contrast, Dyn (1-13) elicited a dose-dependentprolongation of the APD at fM-nM concentrations and required much higherconcentrations (ca. μM) to shorten the APD (n=35).

FIG. 3 illustrates that chronic exposure of a DRG neuron to a bimodallyacting opioid (DADLE) causes the DRG neuron to become supersensitive tothe excitatory effects of dynorphin (1-13) (Dyn), whereas perfusion ofetorphine effectively shortened the APD of the same DRG neuron(inhibitory response). 1: Action potential generated by a DRG neurontreated for 3 wks in culture with 1 μM DADLE and then tested in BSS with1 μM DADLE. 2: APD is prolonged by bath perfusion of 1 fM Dyn with 1 μMDADLE (5 min test). 3,4: APD is further prolonged by sequentiallyraising the Dyn concentration to 1 nM and 1 μM (5 min tests). 5: Controlresponse 5 min after washout of Dyn with BSS containing 1 μM DADLE. 6: 1fM etorphine (Etorp) shortens the APD of the same DRG neuron in thepresence of 1 μM DADLE. 7-9: Further increases in the concentration ofetorphine from 1 pM to 1 μM progressively shorten the APD. 10: APDreturns to control value after removal of etorphine.

FIG. 4 shows that chronic exposure to a bimodally acting opioid (DADLE)followed by acute application of low concentrations of etorphine canblock the excitatory APD-prolonging effects precipitated by naloxone(NLX) in this supersensitive DRG neurons. 1: Action potential generatedby a DRG neuron treated for 2 wks in culture with 1 μM DADLE and thentested in BSS with 1 μM DADLE. 2: 1 nM NLX prolongs the APD of this DRGneuron (5 min test). In contrast, nM naloxone is ineffective on naiveDRG neurons (Crain & Shen, 1992a,b) 3: Acute addition of 1 pM etorphineattenuates the naloxone-induced APD prolongation (5 min test). 4:Further increase in concentration of etorphine to 1 nM almost completelyblocks the naloxone-induced APD prolongation.

FIG. 5 illustrates the relief of naloxone-precipitated, sustained bodyweight loss by morphine, DHE and methadone injections inmorphine-dependent rats. Daily dose: morphine 100 mg/kg, divided into 2subdoses; DHE 12 μg/kg, divided into 4 subdoses; methadone 24 mg/kg,divided into 4 subdoses. Filled circle: morphine group; open circle: DHEgroup; filled triangle: methadone; cross: saline control group. X±SD,***p<0.01, as compared with saline control group.

FIG. 6 depicts the effect of DHE and methadone substitution on naloxoneprecipitated body weight loss is morphine-dependent rats. The bodyweight loss from the first naloxone precipitation test is provided inColumn A. The second naloxone precipitation test was performed after 4days of maintaining one group of rats with morphine (100 mg/kg/day,divided into 2 subdoses), a second group with DHE (12 μg/kg/day, dividedinto 4 subdoses) and a third group with methadone (24 mg/day, dividedinto 4 subdoses). The body weight loss after the second naloxoneprecipitation test is provided in Column B. Statistical p values betweenthe first and second naloxone precipitation test are "**", p<0.05 and"***", p<0.01. The p value for the DHE group relative to the methadonegroup is p<0.05.

FIG. 7 depicts the withdrawal symptom scores after naloxoneprecipitation for DHE and methadone substitution in morphine-dependentrats. Rats were treated as described in FIG. 6. Column A: Withdrawalscores from the first naloxone precipitation test. Column B: Withdrawalscores from the second naloxone precipitation test. Statistical p valuesbetween the first and second naloxone precipitation test are "**",p<0.05 and "***", p<0.01. The p value for the DHE group relative to themethadone group is p<0.01.

FIG. 8 shows the development of withdrawal symptoms inmorphine-dependent monkey after cessation of morphine.

FIG. 9 illustrates the relief of withdrawal symptoms by DHE inmorphine-dependent monkeys. The arrows indicate time of DHE injection (3μg/kg). Open circle: control group; filled circle: DHE group.

FIG. 10 illustrates the therapeutic effect of DHE and methadone onwithdrawal symptoms of morphine-dependent monkeys. The arrows indicatethe time of naloxone (NLX) precipitation (1 mg/kg). Open circle: controlgroup; filled circle: DHE group; filled triangle: methadone group.

BRIEF DESCRIPTION OF ABBREVIATIONS USED

    ______________________________________                                        BRIEF DESCRIPTION OF ABBREVIATIONS USED                                       ______________________________________                                        DADLE     [D--Ala.sup.2,D--Leu.sup.5 ]enkephalin                              DAGO      [D--Ala.sup.2,MePhe.sup.4,                                                    Gly-ol]enkephalin                                                   DPDPE     Tyr--D--Pen--Gly--Phe--D--Pen                                                 (Pen = penicillamine)                                               U-50,488H 3,4 dichloro-N-methyl-N-(2-[1-pyrrolidinyl]-                                  cyclohexyl)benzene-acetamide                                        Dynorphin 1-13                                                                          dynorphin A, Fragment 1-13                                                    (Tyr--Gly--Gly--Phe--Leu--Arg--Arg--                                          Ile--Arg--Pro--Lys--Leu--Lys)                                       Dynorphin 1-17                                                                          dynorphin A, Fragment 1-17                                                    (Tyr--Gly--Gly--Phe--Leu--Arg--Arg--                                          Ile--Arg--Pro--Lys--Leu--Lys--Trp--                                           Asp--Asn--Gln)                                                      Etor      etorphine                                                           DHE       dihydroetorphine                                                    ______________________________________                                    

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, electrophysiologic assay ofthe effects of opioids on the action potential duration of sensoryneurons in organotypic cultures provides an extremely sensitive in vitrobioassay to screen and characterize agonists with the ability toactivate inhibitory, but not excitatory, opioid receptor-mediatedfunctions. This assay permits identification of low- or non-addictiveopioid analgesics as well as agents useful for treatment of drugaddiction.

As used herein "non-addictive" and "low-addictive" are usedinterchangeably to describe the addiction potential of the opioids ofthe present invention. Ill treating opioid addiction in accordance withthe present invention, the subject opioids are essentially non-addictiveat the prescribed dosages when used for periods of up to several weeks.For example, DHE administration to a drug addict in the range of about10 μg to about 1000 μg per day which is gradually withdrawn over aperiod of up to 14 days, does not result in addiction to DHE. Incontrast, even well-controlled treatment of drug addicts by methadonesubstitution invariably results in transfer to methadone addiction. Thepresent invention, thus, greatly improves the present methods fortreating opiate drug abuse without concomitant addiction to anotheropioid.

Likewise, treatment of acute pain for several days with the subjectopioids in accordance with the present invention, does not result inaddiction. While treatment of chronic pain of long duration with thesubject opioids generally does not result in addiction, mild addictionmay result in exceptional cases. Hence use of the subject opioids inaccordance with this invention is non-addictive for the vast majority ofchronic pain patients. The addiction potential of the subject opioids,as illustrated with DHE, for chronic pain patients is thus low, ion,typically less than 1 in 100 for patients treated greater than 3 months.For example, no addiction has been observed in treating patients for upto 3 months with DHE. Moreover, in the rare cases of addiction, suchaddiction may have resulted from minor contaminants present inbimodally-acting thebaine, a starting material for drug synthesis, whichis carried into certain preparations of DHE.

As used herein "opioid" refers to any substance that binds specificallyto an opiate receptor (Casy & Parfitt, 1986; Pasternak 1988).

As used herein "replacement opioid" is a bimodally-acting opioid thathas both inhibitory and excitatory effects on opioid receptors. Suchopioids, generally, have a longer duration of action than thenon-addictive opioid analgesics.

Activation of opioid receptors has been known to produce inhibitoryeffects on neuronal activity which in turn provides the primary cellularmechanism underlying opioid analgesia in vivo (e.g. North, 1986).However:, recent electrophysiological studies indicated that specificmu-, delta- and kappa-opioid receptor agonists elicit both excitatoryand inhibitory modulation of the action potentials of sensory DRGneurons isolated ill culture in a concentration dependent manner (Shen &Crain, 1989; Crain & Shen, 1990).

These opioid agonists were found to elicit excitatory effects at low(<nM) concentrations and inhibitory effects at high (μM) concentrationsas measured by prolongation or shortening of the calcium-dependentcomponent of the action potential duration (APD), respectively (See U.S.Ser. No. 977,332 at FIG. 2 and herein at Table 1).

Earlier experiments demonstrated that the excitatory effects of opioidsare mediated by opioid receptors that are positively coupled via acholera toxin-sensitive Gs-like regulatory protein to adenyl cyclase andcyclic AMP-dependent voltage-sensitive ionic conductances (resembling,for example, beta-adrenergic receptors) (See U.S. Ser. No. 977,332 atFIG. 2; Shen & Crain, 1989, 1990a; Crain & Shen, 1990, 1992), whereasinhibitory effects are mediated by opioid receptors linked to pertussistoxin-sensitive Gi/Go proteins (resembling alpha₂ -adrenergic receptors)(See U.S. Ser. No. 977,332 at FIG. 2; Shen & Crain, 1989; Gross et al,1990).

The ability to differentiate between these bimodal properties ofopioids, i.e. excitatory and inhibitory activities mediated by twodistinct groups of opioid receptors, has led to the present invention,and particularly to a method for identifying low- or non-addictiveopioid analgesics. Hence, this method provides an in vitro bioassay toidentify compounds that can selectively activate the inhibitory but notexcitatory opioid response. Since sustained activation of excitatoryopioid receptor functions plays a crucial role in development oftolerance and dependence in chronic opioid-treated neurons in vitro(Crain & Shen, 1992; Shen & Crain, 1992), compounds with suchproperties, i.e. which activate the inhibitory response but not theexcitatory response, are useful as non-addictive analgesics in vivo.

In particular, the in vitro bioassay uses a cell culture system of DRGneurons to screen candidate compounds by exposing the DRG neurons to thecandidate compound and observing its effect on the APD using standardelectrophysiological recording methods. The detailed methodology forgrowing neurons, treating with a candidate compound and recording theAPD are provided in Example 1. Any opioid compound screened by thisbioassay that exhibits inhibitory effects (e.g., shortening the APD inDRG neurons) but not excitatory effects (e.g., prolonging the APD in DRGneurons) in about the fM-pM range to μM range is a low- or non-addictiveopioid analgesic in vivo. Generally, these compounds effect the APD in aconcentration-dependent manner and the responses are mediated byspecific opioid receptors. Hence, the method of the present inventionprovides a powerful tool to identify low- or non-addictive opioidanalgesics.

Nearly all the opioids tested by this bioassay, including morphine,enkephalins, dynorphins, endorphins and synthetic opioid peptides, havedose-related dual modulatory effects (i.e. both inhibitory andexcitatory effects) on the action potential of sensory DRG neurons. Allsuch compounds are well-known to be addictive. However, in accordancewith this invention etorphine and dihydroetorphine (thebainederivatives) (Bentley and Hardy, 1963; Bentley and Hardy, 1967),compounds previously believed and classified as addictive (WHO Rep1966), have the selective characteristic (Table 1) of inhibitingopioid-receptor mediated functions without exciting such functions. Bothetorphine and dihydroetorphine elicit dose-dependent (inhibitory)shortening of the APD, starting at about pM levels in some of the DRGneurons, and reaching a maximum effect at μM levels in most of the DRGneurons (Example 1). Furthermore, no excitatory prolongation of the APDoccurs with these two compounds at <pM concentrations in contrast to thecharacteristic excitatory effects elicited at low concentration by thebimodally-acting opioids.

It is well known that chronic exposure of DRG-spinal cord explants tobimodally-acting opioids (e.g., morphine or DADLE) causes sensory DRGneurons to become desensitized to the inhibitory effects of opioidagonists, resulting in tolerance (Crain et al, 1988), andsupersensitized to the excitatory effects of opioid agonists as well asantagonists, resembling significant features of abstinence, dependenceand withdrawal syndrome in vivo (Crain & Shen, 1992a,b; Shen & Crain,1992).

Sustained activation of excitatory opioid receptors after chronictreatment with an opioid agonist triggers a positive-feedback mechanismthat results in up-regulation of a Gs/adenylate cyclase/cyclicAMP/protein kinase A/GM1 glycosyl-transferase system that may accountfor the remarkable supersensitivity of chronically opioid-treatedneurons to the excitatory effects of opioid antagonists and agonists(Crain & Shen, 1992a,b; Shen & Crain, 1992).

When DRG-cord explants are chronically treated with a bimodally-actingdelta/mu agonist, DADLE (1 μM) or morphine (1 μg/ml) for 3 weeks, acutetreatment with etorphine still elicits a marked inhibitorydose-dependent shortening of the APD of DRG neurons even atconcentrations as low as 1 fM (Example 2), whereas bimodally-acting mu,delta and kappa opioid agonists show a high degree of opioid excitatorysupersensitivity at concentrations ranging from pM to μM (Example 2).

Furthermore, the excitatory APD prolongation of chronic opioid-treatedDRG neurons precipitated by acute application of nM naloxone (Crain &Shen, 1992a,b), which provides a cellular model of naloxone-inducedwithdrawal supersensitivity in opiate addicts in vivo (Crain & Shen,1992b), can be blocked by acute application of etorphine, but not bymorphine or other bimodally acting opioid agonists (Example 2).

Tissue culture studies provide strong support that excitatory opioidreceptor functions of sensory neurons play important roles in vivo, bothby attenuating analgesic effects mediated by inhibitory opioid receptorsand by facilitating the cellular mechanisms underlying addiction. Theuse of opioids (e.g. etorphine, dihydroetorphine), that at lowconcentrations preferentially activate inhibitory but not excitatoryopioid receptor functions in vitro, as indicated by the screening model,results in much more potent analgesia in vivo and far less evidence ofdependence/addiction than occurs during chronic treatment with morphineand most other bimodally-acting opioids.

The present invention demonstrates that etorphine and compounds withsimilar properties as identified by the present bioassay (e.g.dihydroetorphine) elicit potent dose-dependent inhibitory APD-shorteningeffects on naive and chronic opioid-treated, "addicted" sensory DRGneurons, even at low (pM-nM) concentrations where most bimodally-actingopioids generally elicit excitatory APD-prolonging effects. Henceetorphine and similar compounds of this invention selectively activateinhibitory rather than excitatory opioid receptors on DRG neurons, evenwhen the cells are supersensitive to the excitatory effects ofbimodally-acting opioids following chronic treatment.

Etorphine has long been known to be >1,000 times more potent thanmorphine as an analgesic in animals (Blane et al, 1967) and humans(Blane & Robbie, 1970; Jasinski et al, 1975). This invention shows thatthe high inhibitory potency of etorphine may be due, in part, to itsselective activation of inhibitory opioid receptors whose effects arenot attenuated by the concomitant activation of higher-affinityexcitatory opioid receptors.

The clinical trial results of the present invention show that low dosesof dihydroetorphine, a specifically inhibitory opioid-receptor agonist,are remarkably effective in relieving postoperative pain and chronicpain in terminal cancer patients, yet tolerance and addiction are farless evident than observed with morphine and other conventionalbimodally-acting opioids (Example 5). Thousands of patients have beentreated with a 90% effective rate and no significant adverseside-effects have been observed.

In addition, several hundred heroin addicts have been successfullytreated over a two year period. In this group, withdrawal symptoms wererapidly blocked and dihydroetorphine substitution therapy was maintainedfor about a week with minimal rebound after final opioid withdrawal(Example 6). Similar results were obtained in tests onmorphine-dependent monkeys and rats (Examples 3 & 4). The successfulresults obtained with dihydroetorphine in treating heroin and morphineaddiction are in sharp contrast to the unreliable results obtained incomparative clinical studies with methadone and other bimodally-actingor mixed agonist-antagonist opioids.

Hence, another aspect of the present invention provides a method oftreating opioid addiction by administering a non-addictive opioid oranalog thereof, in an amount effective and for a time sufficient torelieve the withdrawal symptoms of opioid addiction and subsequentlywithdrawing administration of said opioid or analog thereof.

The compounds of the present invention are prepared inter alia by theimproved synthetic methods for the preparation of DHE, etorphine andanalogs of these compounds as described in U.S. Ser. No. 977,332 filedNov. 17, 1992. Moreover, the method for preparing salts, particularlypharmaceutically acceptable salts, of the foregoing compounds is alsoprovided therein.

Another aspect of the invention is directed to pharmaceuticalcompositions containing the opioid compounds of the present inventionincluding dihydroetorphine and its analogues, etorphine and itsanalogues as well as pharmaceutically acceptable salts of any of theforegoing compounds.

Dosage forms (compositions) suitable for administration can contain fromabout 10 μg to about 1000 μg of active ingredient per unit. In thesepharmaceutical compositions the active ingredient will ordinarily bepresent in an amount of about 0.5-95% by weight based on the totalweight of the composition.

The active ingredient can be administered sublingually in solid dosageforms, such as capsules, tablets, and powders, or be administeredparenterally in sterile liquid dosage forms.

Gelatin capsules contain the active ingredient and powdered carriers,such as lactose, sucrose, mannitol, starch, cellulose derivatives,magnesium stearate, stearic acid, and the like. Similar diluents can beused to make compressed tablets. Both tablets and capsules can bemanufactured as sustained release products to provide for continuousrelease of medication over a period of hours. Compressed tablets can besugar coated or film coated to mask any unpleasant taste and protect thetablet from the atmosphere.

In general, water, a suitable oil, saline, aqueous dextrose (glucose),and related sugar solutions and glycols such as propylene glycol orpolyethylene glycols are suitable carriers for parenteral solutions.Solutions for parenteral administration preferably contain a watersoluble salt of the active ingredient, suitable stabilizing agents, andif necessary, buffer substances. Antioxidizing agents such as sodiumbisulfite, sodium sulfite, or ascorbic acid, either alone or combined,are suitable stabilizing agents. Also used are citric acid and its saltsand sodium EDTA. In addition, parenteral solutions can containpreservatives, such as benzalkonium chloride, methyl- or propyl-paraben,and chlorobutanol.

Suitable pharmaceutical carriers are described in Remington'sPharmaceutical Sciences, A. Osol, a standard reference text in thisfield.

Yet another aspect of this invention provides a pharmaceuticalcomposition which comprises a low- or non-addictive opioid analgesic, ora pharmaceutically acceptable salt thereof, in admixture with naloxonewhich is an opioid antagonist. The low- or non-addictive opioidanalgesics are those compounds as provided herein, e.g. etorphine, DHEand the like, in amounts as provided herein. These pharmaceuticalcompositions are provided in formulations as described above.

The subject compositions are thus useful to avoid diversion or abuse oftake-home preparations of solid forms, e.g. tablets of low- ornon-addictive opioid analgesics administered orally or sublingually touses other than detoxification or severe pain relief. Since naloxone haslow oral or sublingual bioavailability, an amount of naloxone can beintroduced into the preparations that has no effect when taken orally orsublingually but antagonizes the effect of the low or non-addictiveopioid analgesic, e.g. DHE, when the preparation is dissolved in waterand injected. The amount of naloxone can be readily determined by one ofordinary skill in the art.

The examples serve to illustrate the present invention and are not to beused to limit the scope of the invention.

REFERENCES CITED

Bentley, K. W. & Hardy, D. G.: New potent analgesics in the morphineseries. Proc. Chem. Soc. p. 220, 1963.

Bentley, K. W. & Hardy, D. G. : Novel analgesics and molecularrearrangements in the morphine-thebaine group. III. Alcohols of the6,14-endo-ethenotetrahydro-oripavine series and derived analogues ofn-allylnormorphine and norcodeine. J. Amer. Chem. Soc. 89: 3281-3286,1967.

Blane, G. F. & Robbie, D. S. : Trial of etorphine hydrochloride (M99Reckitt) in carcinoma pain:preliminary report. Brit. J. Pharmacol.Chemother. 20:252-253, 1970.

Blane G. F., Boura, A. L. A., Fitzgerald, A. E. and Lister, R. E.:Actions of etorphine hydrochloride (M99): A potent morphine- like agent.Brit. J. Pharmac. Chemother. 30:11-22, 1967.

Casy, A. F. & Parfitt, R. T.: Opioid Analgesics: Chemistry andReceptors, Plenum Press, New York, 1986.

Crain, S. M. & Shen, K.-F. : Opioids can evoke direct receptor-mediatedexcitatory effects on sensory neurons. Trends Pharmacol. Sci. 11:77-81,1990.

Crain, S. M. & Shen, K.-F.: After chronic opioid exposure sensoryneurons become supersensitive to the excitatory effects of opioidagonists and antagonists as occurs after acute elevation of GM1ganglioside. Brain Res. 575:13-24, 1992a.

Crain, S. M. & Shen, K.-F. : After GM1 ganglioside treatment of sensoryneurons naloxone paradoxically prolongs the action potential but stillantagonizes opioid inhibition. J. Exp. Pharmacol. Ther. 260:182-186,1992b.

Crain, S. M., Shen, K.-F. & Chalazonitis, A.: Opioids excite rather thaninhibit sensory neurons after chronic opioid exposure of spinalcord-ganglion cultures. Brain Res. 455:99-109, 1988.

Deneau, G. A. & Seevers, M. H.: Drug dependence. In: Lawrence D. R.,Bacharach, A. L. eds. Evaluation of Drug Activities: Pharmacometrics.Vol. 1, London: Academic Press, 1964, pp. 167-179.

Gross, R. A., Moises, H. C., Uhler, M. D. & Macdonald, R. C.: DynorphinA and cAMP-dependent protein kinase independently regulate neuronalcalcium currents. Proc. Natl. Acad. Sci. 87:7025-7029, 1990.

Huang, M & Qin, B. Y.: Acta Pharmacol. Sinica, 3(1):9, 1982.

Jaffe, J. H.: Drug addiction and drug abuse. in The PharmacologicalBasis of Therapeutics, 8th ed. (eds. Gilman, A. G., Rall, T. W., Nies,A. S. & Taylor, P.) Pergamon Press, N.Y. pp. 522-573, 1990.

Jasinski, D. R., Griffith, J. D. & Carr, C. B. : Etorphine in man 1.Subjective effects and suppression of morphine abstinence. Clin.Pharmacol. Ther. 17:267-272, 1975.

Pasternak, G. W.: The Opiate Receptors, Humana Press, New Jersey, 1988.

Shen, K.-F. & Crain, S. M.: Dual opioid modulation of the actionpotential duration of mouse dorsal root ganglion neurons in culture.Brain Res. 491:227-242, 1989.

Shen, K.-F. & Crain, S. M. : Cholera toxin-A subunit blocks opioidexcitatory effects on sensory neuron action potentials indicatingmediation by Gs-linked opioid receptors. Brain Res. 525:225-231, 1990.

Shen, K.-F. & Crain, S. M. : Chronic selective activation of excitatoryopioid receptor functions in sensory neurons results in opioid"dependence" without tolerance. Brain Res. (in press), 1992.

Wei, E., Loh, H. H. & Way, E. L.: Quantitative aspects of precipitatedabstinence in morphine-dependent rats. J. Pharmacol. Exp. Therap.184:398-403, 1973.

W. H. O. Expert Committee on Dependence-Producing Drugs, WHO Tech. Rep.Ser. Vol 343, p. 5, 1966.

Winger, G., Skjoldager, P. & Woods, J. H. : Effects of buprenorphine andother opioid agonists and antagonists on alfantanil- andcocaine-reinforced responding in Rhesus monkey. J. Pharmacol. Exp.Therap. 261:311-317, 1992.

EXAMPLE 1 Selective Inhibitory but Not Excitatory Effect of Etorphineand Dihydroetorphine on the Action Potential Duration of Sensory DorsalRoot Ganglion Neurons in Culture

Tissue culture:

The experiments were carried out on dorsal root ganglion (DRG) neuronsin organotypic explants of spinal cord with attached DRGs (from13-day-old fetal mice) after 3 to 5 weeks of maturation in culture. TheDRG-cord explants were grown on collagen-coated coverslips in Maximowdepression-slide chambers. The culture medium consisted of 65% Eagle'sminimal essential medium, 25% fetal bovine serum, 10% chick embryoextract, 2 mM glutamine and 0.6% glucose. During the first week invitro, the medium was supplemented with nerve growth factor (NGF-7s) ata concentration of about 0.5 μg/ml to enhance survival and growth of thefetal mouse DRG neurons.

Electrophysiological recordings:

The culture coverslip was transferred to a recording chamber containingabout 1 ml of Hanks' balanced salt solution supplemented with 5 mM Ca²⁺and 5 mM Ba²⁺ (BSS) to provide a prominent baseline response forpharmacological tests. Intracellular recordings were obtained from DRGperikarya selected at random within the ganglion with micropipetteprobes. The micropipettes were filled with 3M KCl (resistance about60-100 megohms) and were connected via a chloridized silver wire to aneutralized input capacity preamplifier (Axoclamp 2A) for current clamprecording. After impalement of a DRG neuron, brief (2 msec) depolarizingcurrent pulses were applied via the recording electrode to evoke actionpotentials (at a frequency of 0.1 hz). Recordings of the actionpotentials were stored on a floppy disc using the p-clamp program (AxonInstruments) in a microcomputer (IBM AT-compatible).

Drug test:

Drugs were applied by bath perfusion with a manually operated push-pullsyringe system at a rate of 2-3 ml/min. Perfusion of test agents wasbegun after the action potential and the resting potential of the neuronreached a stable condition during >4 min pretest periods in control BSS.Opioid-mediated changes in the APD were considered significant if theAPD alteration was >10% of the control value for the same cell and wasmaintained for the entire test period (about 5 min). The APD wasmeasured as the time between the peak of the APD and the inflectionpoint on the repolarizing phase.

Opioid Responsiveness:

The opioid responsiveness of DRG neurons was analyzed by measuringopioid-induced alterations in the APD of DRG perikarya. DRG neurons inDRG-cord explants were examined for sensitivity to acute application ofetorphine or dihydroetorphine at fM to μM concentrations. None of thecells (n=12) showed APD shortening or prolongation in 1 fM etorphine.However, naloxone-reversible APD shortening was observed in 25% of thecells (n=8) after application of pM and nM concentrations of etorphineand in 100% of the cells (n=7) after application of μM concentrations ofetorphine (FIGS. 1 and 2). None of the DRG neurons tested with differentconcentrations of etorphine (n=13) showed APD prolongation.

These results are in sharp contrast to other mu, delta or kappa opioids(e.g. morphine, methadone, DAGO, DPDPE, DADLE, dynorphin (amino acids1-13) or (amino acids 1-17) and U-50,488H), each of which show bimodalaction such that low concentrations (<nM) evoked excitatoryAPD-prolonging effects and higher concentrations ( μM) evoked inhibitoryAPD-shortening effects on many DRG neurons (FIG. 2; Table 1). For FIG.2, data were obtained from 11 neurons for etorphine test, half of whichwere tested with all four concentrations of etorphine (from fM to μM).

Like etorphine, electrophysiologic tests with dihydroetorphine (overfM-μM ranges) on DRG neurons (n=15) showed concentration-dependentinhibitory APD shortening effects, with threshold at fM-pM, and noevidence of excitatory APD prolonging effects (FIG. 2).

                  TABLE 1                                                         ______________________________________                                        Alteration of action potential duration of dorsal root ganglion               neurons treated with high and low concentrations of opioids.                               Alteration of                                                                 Action Potential Duration                                                     Opioid at low                                                                          Opioid at high                                                       concentration                                                                          concentration                                                        <nM      μM                                                   ______________________________________                                        Morphine       Prolongation                                                                             Shortening                                          DAGO           Prolongation                                                                             Shortening                                          DADLE          Prolongation                                                                             Shortening                                          DPDPE          Prolongation                                                                             Shortening                                          U-50,488H      Prolongation                                                                             Shortening                                          Dynorphin 1-13 Prolongation                                                                             Shortening                                          Dynorphin 1-17 Prolongation                                                                             Shortening                                          Met-enkephalin Prolongation                                                                             Shortening                                          Leu-enkephalin Prolongation                                                                             Shortening                                          β-endorphin                                                                             Prolongation                                                                             Shortening                                          Methadone      Prolongation                                                                             Shortening                                          Fentanyl       Prolongation                                                                             Shortening                                          Levorphenol    Prolongation                                                                             Shortening                                          Thebaine       Prolongation                                                                             Shortening                                          Etorphine*     Shortening Shortening                                          Dihydroetorphine*                                                                            Shortening Shortening                                          ______________________________________                                         *Selectively activate inhibitory (APD) shortening), but not excitatory,       opioid receptormediated functions.                                       

EXAMPLE 2

Enhanced Inhibitory Effect of Etorphine on Chronic Opioid-Treated,Addicted Sensory Neurons that had become Supersensitive to theExcitatory Effects of Bimodally Acting Opioid Agonists and to Naloxone

Drug tests:

Mouse DRG-cord explants, grown for >3 weeks as described in Example 1,were chronically exposed to the bimodally acting (excitatory/inhibitory)delta/mu opioid agonist, DADLE (3 μM) or morphine (1 μM) for 1 week orlonger. Electrophysiological recordings were made as in Example 1.

Results:

After such chronic exposure, DRG neurons are supersensitive to theexcitatory effects of opioids (Crain & Shen 1992a; Shen & Crain, 1992).Whereas pM-nM Dyn (amino acid 1-13) is generally required to prolong theAPD of naive DRG neurons (FIG. 2), fM levels and lower are effective atprolonging the APD after chronic opioid treatment (FIG. 3, traces 1-4).In contrast, acute application of etorphine to chronic DADLE-treatedneurons effectively shortened the APD of the same DRG neurons thatshowed supersensitive excitatory responses to low concentrations ofbimodally-acting opioids (FIG. 3, traces 6-9). Furthermore, theinhibitory APD-shortening effect of etorphine on DRG neurons appears tobe significantly enhanced. While pM etorphine was effective inshortening the APD of 25% of the DRG neurons tested in naive explants(FIGS. 1 and 2), this low opioid concentration was effective in all ofthe chronic DADLE-treated DRG neurons tested in the presence of 1 μMDADLE (n=4; FIG. 3, traces 5 and 6). This same low concentration ofetorphine (pM) was effective in 71% of the chronic morphine-treated (1μg/ml) DRG neurons tested in the presence of 1 μg/ml morphine (n=7).Dose response tests on chronic DADLE-treated DRG neurons showed, infact, that the magnitude of the APD was progressively shortened when theacute etorphine concentration was increased sequentially from 1 fM to 1μM (FIG. 3, traces 6-9).

The opioid antagonist, naloxone (nM-μM), does not alter the APD of naiveDRG neurons (Crain & Shen 1992a, b). In contrast, after chronic opioid,such as DADLE treatment, acute application of low concentrations ofnaloxone prolongs the APD of sensory neurons (Crain et al, 1992b; Shen &Crain, 1992). The naloxone-induced excitatory APD-prolonging effect onchronic opioid-treated DRG neurons is shown in FIG. 4, traces 1 and 2.Acute application of low concentrations of etorphine effectively blocksthe naloxone-induced APD prolongation of DRG neurons (n=3; FIG. 4,traces 3 and 4) whereas bimodally acting opioids are ineffective.

Since etorphine and dihydroetorphine elicit potent inhibitory effects onnaive sensory neurons even when applied at extremely low (pM)concentrations and show no signs of concomitantly activating excitatoryopioid receptors on these cells, these in vitro electrophysiologicanalyses predict that application of etorphine and dihydroetorphine invivo at the relatively low doses required to produce analgesia (<1,000times lower than morphine) are not addictive even after sustainedapplication for treatment of chronic pain.

EXAMPLE 3 Suppression of Withdrawal Symptoms by DHE inMorphine-Dependent Rats

Morphine-dependent rat model:

Wistar rats of both sexes, 120-150 g body weight, were administeredmorphine subcutaneously (s.c.) twice a day (8:00 a.m., 4:00 p.m.)starting at a dose of 20 mg/kg/day, with an increment of 20 mg/kg/dayfor 5 consecutive days until the final dose reached 100 mg/kg/day.

Naloxone (NLX) precipitation for the scoring of withdrawal symptoms:

3-4 hrs after administering the last dose of morphine (or other testdrug (s)), withdrawal symptoms of morphine-dependent rats wereprecipitated by intraperitoneal (i.p.) injection of naloxone (4 mg/kg).Naloxone-induced withdrawal symptoms were monitored for 1 hr thereafterand scored according to the method of Wei et al, 1973.

Animal groups:

After 5 days of morphine addiction, the animals were divided into 7groups according to Table 2. Each group contained 5-6 rats.

Groups 1, 2, and 3 received 20 mg/kg morphine (4 times the ED₅₀ foranalgesia), 9 mg/kg methadone (9 times the ED₅₀ analgesia) or 6 μg/kgDHE (12 times the ED₅₀ analgesia) by i.p. injection, respectively. Theseopioid agonists were injected 15-30 min before naloxone precipitationwas initiated. After the naloxone withdrawal test was completed, groups1, 2, and 3 were continued on morphine 100 mg/kg (s.c.) for another 4consecutive days. A second naloxone precipitation test was given on the4th day but only saline was administered (i.p.) prior to naloxone.

The first naloxone precipitation test was performed on the animals ofgroups 4, 5, and 6 in the same manner as for groups 1-3, except theadministration of opioid agonists 15-30 min prior to the naloxone test.For the second naloxone test, groups 4, 5 and 6 received 100 mg/kgmorphine (s.c.) twice a day, 3 μg/kg DHE 4 times a day, or 6 mg/kgmethadone, 4 times a day, instead of morphine at 100 mg/kg, for 4 days,respectively. The second naloxone test was performed as above on the 4thday.

After the first naloxone precipitation test, Group 7 animals were givensaline (s.c.) as control for 4 days before the second naloxone test.

The body weight of the animals was monitored during the entire period.

Results:

One to 2 min after intraperitoneal injection of naloxone, themorphine-dependent rats began to show naloxone induced withdrawalsymptoms with a peak response occurring within 15 min. An hour later thebody weight of the animals was greatly reduced. Intraperitonealinjection of morphine (20 mg/kg), DHE (6 μg/kg) or methadone (9 mg/kg)prior to the administration of naloxone suppressed the naloxone inducedwithdrawal symptoms of the rats. No significant differences insuppressing effect were detected among these three opioid substitutes.For morphine, DHE and methadone, prevention of body weight loss was43.5%, 49.8% and 48.15%, respectively, and suppression of otherwithdrawal symptoms was scored as 45.5%, 63.7% and 49.4%, respectively.

After naloxone precipitation, the body weight of the dependent ratscontinued to decrease. The loss of body weight reached its maximum 24 hafter naloxone precipitation. A gradual weight recovery was achieved by90 h.

Subcutaneous injection of morphine, DHE or methadone was given forseveral days after the first naloxone precipitation test. The loss ofbody weight of morphine-dependent rats was found to be reduced in allthree groups treated with opioid agonists. Subcutaneous administrationof morphine (one hour after naloxone precipitation) reversed the bodyweight loss in 3 hours, with occasional weight gain in some of the rats.A complete recovery of weight loss was observed 48 h later. The effectof subcutaneous injection of DHE or methadone on body weight loss wasnot as dramatic as with morphine. However, both opioids did preventfurther body weight loss. When compared with the untreated control group(saline injected), the effect of both DHE or methadone on body weightloss was highly significant (FIG. 5).

After the first naloxone precipitation test, some of the animalscontinued to be maintained on morphine (s.c.). Four days later, a secondnaloxone test was given. The second naloxone test resulted in moresevere withdrawal symptoms relative to the first test. In contrast, inthose animals that were treated with DHE (s.c., 4 days) instead ofmorphine, the second naloxone test failed to precipitate any withdrawalsymptoms except minor loss in body weight. In the animals maintainedwith methadone (s.c., 4 days), the second naloxone injectionprecipitated less severe withdrawal symptoms in comparison to themorphine group, yet more severe when compare with the DHE group (FIGS. 6and 7).

                                      TABLE 2                                     __________________________________________________________________________    Animal Groups Used to Test the Suppression of NLX-induced                     Withdrawal Symptoms by Different Opioids                                          Development of    Continued                                                   Morphine                                                                              Pretreatment                                                                         1st                                                                              Maintenance with                                                                         Pretreatment                                                                         2nd                                   Animal                                                                            Dependence                                                                            (15-30' prior                                                                        NLX                                                                              Opioids    (15-30' prior                                                                        NLX                                   Groups                                                                            5 days  to 1st test)                                                                         Test                                                                             4 days     to 2nd test)                                                                         Test                                  __________________________________________________________________________    1   Morphine                                                                              Morphine                                                                             NLX                                                                              Morphine 100 mg/kg                                                                       Saline NLX                                       20→100 mg/kg                                                                   (20 mg/kg)                                                        2   Same as 1                                                                             Methadone                                                                            NLX                                                                              Same as 1  Saline NLX                                               (9 mg/kg)                                                         3   Same as 1                                                                             DHE    NLX                                                                              Same as 1  Saline NLX                                               (6 μg/kg)                                                      4   Same as 1                                                                             --     NLX                                                                              Morphine 50 mg/kg                                                                        --     NLX                                   5   Same as 1                                                                             --     NLX                                                                              DHE 3 μg/kg                                                                           --     NLX                                   6   Same as 1                                                                             --     NLX                                                                              Methadone 6 mg/kg                                                                        --     NLX                                   7   Same as 1                                                                             --     NLX                                                                              Saline     --     NLX                                   __________________________________________________________________________

EXAMPLE 4 Anti-Addictive Effects of DHE Treatment of Morphine-DependentMonkeys

Morphine-dependent monkey model:

Seven male rhesus monkeys (Macaca mulatta, 3.4-5 kg) were injected withmorphine (s.c.) twice a day (8:00 a.m., 4:00 p.m.), startling at a doseof 10 mg/kg/day and increasing the dose by increments of 5 mg/kg/dayevery third day until the dosage reached 50 mg/kg/day on the 24th day.This dosage was continued for another 10 days prior to performing drugtests.

Stage 1 drug tests:

The monkeys were randomly divided into 2 groups. At 24 h afterwithdrawal of morphine, Group A (4 animals) received 3 μg/kg DHE (s.c.)every 3 h. The interval between DHE administration was increasedgradually so that by the 3rd day, DHE was only given twice a day, andthen stopped for 2 days of observation. Group B (3 animals) was treatedthe same manner as group A except, this group received saline instead ofDHE. After completion of these tests, all the animals were treated withmorphine for 12 consecutive days by administration of 50 mg/kg/daymorphine (s.c.) twice a day. The test was repeated except the Group Amonkeys received the saline controls and the Group B monkeys receivedthe DHE treatment. Withdrawal symptoms of the animals were observed andscored according to Deneau & Seevers (1964), during the entireexperimental period.

Sixteen hours after withdrawal of morphine, withdrawal symptoms began toappear in the morphine-dependent monkeys. Symptoms were moderate atfirst and included yawning, salivation, agitation and fear. These signsbecame more severe as time went on. Within 20-60 h after withdrawal ofmorphine, the animals' withdrawal symptoms included vomiting, tremor,teeth-gritting on chain, eye closing, lying on its side and dyspnea. Allthese symptoms are indicative of extreme agitation. After 60 h thesesymptoms gradually subsided. By 120 h after withdrawal of morphine, somemoderate withdrawal symptoms were still detected (FIG. 8). One weeklater all the withdrawal symptoms had disappeared.

In sharp contrast, all of these withdrawal symptoms were completelysuppressed by DHE one minute after its administration (3 μg/kg. s.c.).Two and a half to three hours later, withdrawal symptoms reappearedwhich were again suppressed by another dose of DHE (FIG. 9). Thissuppressing effect of DHE on morphine withdrawal symptoms was observedwith each monkey. DHE continued to be effective at suppressingwithdrawal symptoms for 3-4 days with repeated injections at 2.5-3 hintervals. Discontinuation of DHE injection at 80 h after morphinewithdrawal did not trigger any withdrawal symptoms, indicating that theanimals had not become dependent on DHE during this substitutiontreatment.

Stage 2 drug tests:

After the stage 1 experiments, all 7 monkeys were administered morphine(s.c.) at a dose of 50 mg/kg/day for 7 days. The morphine-addictedmonkeys were then randomly divided into 3 groups. Group 1 was maintainedwith s.c. injection of 25 mg/kg morphine twice a day for 9 days. Group 2was substituted with DHE by s.c. injection of 3 μg/kg DHE(equi-analgesic dose) four times a day for 4 days, of 1.5 μg/kg DHEthree times a day for 2 days and then twice a day for 3 days. Group 3was substituted with methadone by s.c. injection of 6 mg/kg methadone(equi-analgesic dose) four times a day for 4 days, of 3 mg/kg threetimes a day for 2 days and then twice a day for 3 days.

Sixteen hours after the last injection of opioid, each animal wasprecipitated with naloxone (1 mg/kg, s.c.) to evaluate the severity ofnaloxone withdrawal symptoms for 1 day. Seven days later, anothernaloxone precipitation test was performed on these monkeys for 1 day.After completion of all tests, 3 monkeys were randomly selected formorphine addiction (25 mg/kg, s.c., twice a day for 7 days). Naloxoneprecipitation tests were performed twice on these 3 monkeys, the firsttrial given after the last injection of morphine and the second trialgiven 7 days thereafter.

Since the action period of DHE and methadone is relatively short, somemoderate withdrawal symptoms appeared during the 6 hr intervals betweeninjections on the first 3 days. After these 3 days, the withdrawalsymptoms became milder and gradually disappeared.

Naloxone precipitation tests were carried out after 9 days ofsubstitution treatment with DHE or methadone. For the monkeys maintainedon morphine, naloxone injection precipitated a series of withdrawalsymptoms after 15 sec. These symptoms included squeaking, coughing,rolling, tremor, vomiting, agitation, teeth-gritting on chain, dyspnea,and finally lying down on the ground. The animals recovered by 7 dayslater. The monkeys substituted with methadone showed moderate naloxonewithdrawal symptoms including yawning, placing hands on the belly,tremor of extremities, frequent teeth-gritting on chain and agitation.However, those animals substituted with DHE showed no change in behaviorboth before and after naloxone precipitation. Table 3 shows the scoresof naloxone withdrawal symptoms from the 3 different groups of monkeys.Once morphine was fully excreted from the body (7 days afterwithdrawal), naloxone no longer precipitated any withdrawal symptoms.

The naloxone precipitation test was used to evaluate whether theseanimals were dependent on morphine or had become dependent on thesubstitution opioid.

FIG. 10 illustrates the variations in the scores of withdrawal symptomsin monkeys after DHE or methadone substitution relative to compulsivewithdrawal. In the compulsive withdrawal group (upper trace) withdrawalsymptoms reached a maximal score during the first several days, butreturned to zero by 7 days after abrupt morphine withdrawal. On day 9,naloxone no longer precipitated any withdrawal symptoms. For themethadone substitution group (middle trace), the withdrawal symptomsduring the first several days were partially suppressed. On day 9,naloxone precipitated withdrawal symptoms, suggesting that the animalshave already switched to methadone dependence. For DHE substitutiongroup (lower trace) only minor withdrawal symptoms were observed.Naloxone precipitation tests on day 9 did not trigger any withdrawalsymptoms. These results indicate that DHE is an ideal low- ornon-addictive substitution drug for treatment of opioid abstinenceproblems.

                  TABLE 3                                                         ______________________________________                                        Scores of naloxone withdrawal syndromes in                                    morphine dependent monkeys with or without                                    DHE or methadone substitution treatment                                                    Scores of withdrawal syndromes                                                ( X ± SD)                                                     Treatment.sup.a                                                                              1st naloxone                                                                             2nd naloxone                                        (n)            precipitation.sup.b                                                                      precipitation.sup.c                                 ______________________________________                                        morphine (4)   49.0 ± 2.2                                                                            1.5 ± 1.0                                        DHE (3)         2.0 ± 1.0***                                                                         1.0 ± 1.0                                        methadone (3)  17.0 ± 4.6***                                                                         1.3 ± 1.2                                        ______________________________________                                         .sup.a Daily treatment dosages were 50 mg/kg morphine (divided into 2         subdoses), 12 μg/kg DHE (divided into 4 subdoses) decreased to 3           μg/kg (divided into 2 subdoses), and 24 mg/kg methadone (divided into      subdoses) decreased to 6 mg/kg (divided into 2 subdoses).                     .sup.b The first naloxone precipitation test was performed 16 h after the     last injection of opioid.                                                     .sup.c The second naloxone precipitation test was performed 7 days after      the last injection of opioid.                                                 ***p < 0.01, compared to the morphine group. For the DHE group compared t     the methadone group, then p < 0.01.                                      

EXAMPLE 5 DHE Elicits Potent Low- or Non-Addictive Analgesia in Acuteand Chronic Pain Patients

The results in the first stage clinical trial showed that none of the 20volunteers had euphoria feeling after DHE administration throughsublingual route at 60 μg single dose. At high dosage (e.g. >1 mg perday), dizziness, nausea, vomiting and lethargy appeared. The resultsfrom second stage clinical trial demonstrated that DHE can effectivelyrelieve postoperative pain and pain caused by terminal stage of cancer.The effective rate of 730 cases that have complete medical records was97.6%. Among them, the effective rate of acute pain in patients fromdepartments of surgery, obstetric and gynecology approached nearly 100%.The effective rate for relief of chronic severe pain and terminal stageof cancerous pain was 90-95%. The clinical data indicate that theanalgesic effect of DHE is substantial with only mild side effects. DHEtreatment was effective in those terminal stage cancer patents that wereunresponsive to morphine or pethidine (demerol) treatment. No crosstolerance to DHE was found in these patients. Long-term use of DHE canresult in tolerance; however, the degree of tolerance is less than thatobserved with morphine or pethidine.

Clinical treatment with DHE has been conducted in more than one hundredthousand patients in China. As an analgesic, the main disadvantage ofDHE is its short action period (about 3-4 hours). Compared withmorphine, DHE has high analgesic effect and low addictivity, whereasmorphine has relatively low analgesic effect and high addictivity.During many years of trials using DHE as an analgesic, no cases of drugabuse were ever reported. This phenomena may be attributed to the strictregulation of DHE treatment. The medication period for ordinary pain istypically limited to 1 week; whereas, for patients with terminal cancerpain, the treatment period is much longer. Although some of the patientsbecame tolerant to DHE after long-term use, there is a slight chancethat a few patients may become addicted to the drug after long-term use(e.g., >6 months).

EXAMPLE 6 DHE Substitution Treatment Suppresses Withdrawal Symptoms inOpiate Addicts without Concomitant DHE Addiction

General protocol:

Institution of DHE therapy as a substitute drug began with a sufficientdose on days 1-3 to suppress completely the withdrawal symptoms. On days4-7, the dosage was reduced and by days 8-10 the DHE substitutiontherapy was terminated. This protocol was followed because (1)withdrawal symptoms are most severe during the first 3 days after abruptwithdrawal of heroin or other addictive opioid; (2) withdrawal symptomsgradually decline and disappear after 7-10 days; and (3) consecutive useof DHE as a substitution agent for 7-10 days does not produce anyself-dependence.

DHE administration:

More than 300 cases of chronic heroin users were treated for 7-10 dayswith DHE in 10 hospitals in China. DHE was administered eithersublingual in tablet form (40 μg) or by intramuscular injection (20 μg)or by intravenous dripping (20 μg). The tablet form was used more often.At the onset of withdrawal symptoms, sublingual administration of 1-2tablets (20-40 μg) of DHE effectively suppressed the symptoms. Sustainedsuppression of withdrawal symptoms required repeated DHE medicationevery 2-4 h. Total dosage, was adjusted according to the severity of thewithdrawal symptoms. Typically after 4 days of DHE medication, thedosage required to suppress withdrawal symptoms was generally reduced.The entire course of DHE substitution was generally 7 days. (In oneinstance of overdose of DHE, respiratory side effects occurred.)

For addicts whose withdrawal symptoms were so severe and violent thatsublingual medication was not enough to subdue them, intramuscularinjection of DHE (20 μg) gave instant relief. The addict generallybecame quiet and cooperative. However, to maintain the therapeuticeffect, it was necessary to administer DHE by intravenous dripping (100μg in 500 ml glucose saline for 6-10 hr). The transfusion rate dependedupon the severity of symptoms: the drip rate was increased when thepatient showed sign of restlessness or decreased when the patient wasquiet and complained of lethargy. In severe cases, intravenoustransfusion of DHE was maintained for 3-4 days with progressive decreasein dosage. On day 4 or 5, intravenous dripping of DHE was converted tosublingual DHE administration and terminated on day 7. Occasionallytreatment was prolonged to 8-9 days, but never more than 10 days toprevent possible occurrence of dependence. Hence, by using this optimal7-10 day treatment period DHE is effectively employed as a substitutefor drug addiction therapy.

The effectiveness of DHE substitution therapy was evaluated on day 10 bythe naloxone precipitation test (0.4-0.8 mg naloxone, intramuscularinjection) and urine analysis of the residual amount of opioid. Thetreatment course was considered successful if both tests were negative.

One of the primary advantages of DHE over methadone substitution therapyis the early onset of DHE effectiveness. Withdrawal symptoms weremarkedly relieved after 10-20 min of sublingual administration or 5 minof intramuscular injection of DHE. In contrast, with methadonesubstitution the first dose usually begins at 10 mg and is increasedevery hour until the therapeutic effect is achieved. Such treatment canlast from one to several hours before symptomatic relief. This period isintolerable to a patient with severe withdrawal symptoms. Furthermore,methadone substitution therapy often results in the rebound ofwithdrawal symptoms, suggesting dependence on methadone.

In contrast, cessation of DHE administration generally proceededsmoothly. As with methadone, the side effects of DHE were negligibleduring substitution treatment for drug addiction. Since DHE is shortacting (only 2-4 hr), frequent administration may be necessary. To avoidthis, intravenous dripping of DHE is recommended. However, intravenousadministration can only be prescribed in the hospital and is notapplicable to the ordinary drug rehabilitation clinic. Since methadoneis effective orally (once or twice a day), one alternative is to combineDHE and methadone treatments. For example, DHE is used initially forswift control of the withdrawal symptoms and is then replaced bymethadone to maintain the suppressing effect for 2-3 days. The treatmentis then switched back to DHE on a decreasing dosage regime until DHE isno longer needed (usually another 5-10 days). This combined therapy issafe, pragmatic and convenient.

EXAMPLE 7 Preparation of Various Dihydroetorphine (DHE) Salts andAnalysis of Duration and Potency of the Analgesic Effects Thereof

A total of 26 dihydroetorphine (DHE) salts were prepared according tostep (e) of Example 7 of U.S. Ser. No. 977,332, filed Nov. 17, 1992except the various acids listed below were substituted for HCl.

I. Structures of 26 acids employed to form derivatives ofdihydroetorphine salts ##STR1##

A "mouse hot plate" (55° C.±0.5° C.) method as previously described(Huang and Qin, 1982) was used to score % analgesia to measure thepotency of each DHE salt which was injected to animals subcutaneously.The ED₅₀ (the dose that gives rise to 50% analgesia as calculated by thefollowing formula) was measured for the DHE salts shown in Table 4.##EQU1##

A dose of 5 ED₅₀ was used for each salt to measure the correspondinganalgesic duration. "Analgesia %" was recorded at 90, 120 and 150 minafter administration (Table 5).

In summary, an ED₅₀ (μg/kg) in time range of 0.50 to 2.0 was observedwith the 12 DHE salts tested, indicating an equivalent level ofanalgesic effect: conferred by these salts (see data presented in Table4). Furthermore, except for acetyl DHE, DHE maleate, and DHE amygdalate,all DHE salts demonstrated an equivalent level of analgesia over a120-150 min duration.

                  TABLE 4                                                         ______________________________________                                        Analgesic Effect of Various DHE Salts                                         Salts of DHE.sup.a    ED.sub.50 (μg/Kg)                                    ______________________________________                                        DHE hydrochloride     1.43                                                    Acetyl DHE (27)       0.47                                                    DHE maleate (10       0.58                                                    DHE succinate (2)     0.83                                                    DHE oxalate (1)       0.68                                                    DHE acetate (3)       0.51                                                    DHE malate (4)        0.62                                                    DHE asparagate (25)   1.12                                                    DHE glutamate (26)    0.65                                                    DHE amygdalate (15)   0.61                                                    DHE dibenzoylhydroxyl acetate (16)                                                                  1.29                                                    DHE citrate (7)       1.73                                                    ______________________________________                                         .sup.a The numbers following each salt correspond to the numbered             compounds of Example 7                                                   

                  TABLE 5                                                         ______________________________________                                                  Analgesia % (x ± SD)                                             Salts of DHE                                                                              90 min     120 min    150 min                                     ______________________________________                                        DHE hydrochloride                                                                         42.39 ± 31.34                                                                         20.05 ± 10.91                                                                         28.49 ± 14.21                            Acetyl DHE   5.96 ± 12.65                                                                         8.85 ± 9.47                                                                           ND                                          DHE maleate 15.84 ± 13.82                                                                         ND         ND                                          DHE succinate                                                                             26.16 ± 14.86                                                                         30.77 ± 42.35                                                                         32.26 ± 35.89                            DHE oxalate 14.21 ± 6.37                                                                          19.35 ± 24.14                                                                         ND                                          DHE acetate 21.64 ± 10.11                                                                         29.54 ± 30.93                                                                         ND                                          DHE malate  26.92 ± 23.75                                                                         22.36 ± 19.29                                                                         ND                                          DHE asparagate                                                                            40.96 ± 37.28                                                                         35.94 ± 45.06                                                                         21.44 ± 35.68                            DHE glutamate                                                                             29.33 ± 36.15                                                                          9.27 ± 12.57                                                                         14.09 ± 17.07                            DHE amygdalate                                                                            29.15 ± 26.73                                                                         1.87 ± 2.97                                                                           ND                                          DHE dibenzoylhy-                                                                          45.01 ± 49.66                                                                         13.85 ± 17.49                                                                         ND                                          droxyl acetate                                                                DHE citrate 56.12 ± 46.42                                                                         25.95 ± 37.46                                                                         14.27 ± 14.49                            ______________________________________                                    

EXAMPLE 8

The pharmaceutical preparations of dihydroetorphine hydrochlorideinclude a parenteral injectable sterile solution and a sublingualtablet.

(a) Preparation of injectable dihydroetorphine hydrochloride

This injectable is a pharmaceutical preparation in a sterile aqueoussolution. Its outward appearance is transparent and colorless. Eachampule contains 20 μg of said compound as the active ingredient in 1 mLof solution.

The prescription is shown as follows:

    ______________________________________                                        Dihydroetorphine hydrochloride                                                                       20 mg                                                  0.001 N Hydrochloric acid                                                                            q.s. 1000 mL                                           ______________________________________                                    

(b) Preparation of dihydroetorphine hydrochloride sublingual tablet

The outward appearance of the sublingual tablet is white. Each tabletcontains 20 μg or 40 μg of said compound as active ingredient.

For example, the prescription for 10000 tablets at 40 μg per tablet isas follows:

    ______________________________________                                        Dihydroetorphine hydrochloride                                                                           400    mg                                          Lactose:starch:mannitol:sucrose (3:1:3:3)                                                                600    g                                           Sodium carboxymethyl cellulose (1% aque sol'n)                                                           18     mL                                          Ethyl alcohol (50%)        24     mL                                          Magnesium stearate         6      g                                           ______________________________________                                    

According to the above-mentioned prescription, a designated amount ofdihydroetorphine hydrochloride was weighed and dissolved in 50% ethylalcohol. This solution was added dropwise onto excipients undermechanical stirring to ensure uniformity. Meanwhile, 1% sodiumcarboxymethyl cellulose solution was added dropwise. The soft materialthus formed was screened through a 20-mesh sieve and the same operationwas repeated for 3 times. The product was then dried in an oven at 60°C. Magnesium stearate was added as a lubricating agent for the tablets.

We claim:
 1. A method of treating opioid addiction which comprisesadministering sublingually, intramuscularly or intravenously aneffective amount of a non-addictive opioid analgesic selected from thegroup consisting of etorphine and dihydroetorphine, to a patient for afirst time sufficient for immediate relief or suppression of withdrawalsymptoms due to said opioid addiction; administering an effective amountof an replacement opioid for a second time sufficient to maintain saidrelief or said suppression; followed by administering decreasing amountsof said non-addictive opioid analgesic for a third time sufficient towean said patient from said analgesic.
 2. The method of claim 1 whereinsaid replacement opioid is methadone.
 3. The method of claim 1 whereinsaid amount of said analgesic is from about 10 μg to about 1000 μg perday.
 4. The method of claim 1 wherein said amount of said replacementopioid is from 5 to about 100 mg/day.
 5. The method of claim 2 whereinsaid amount of said analgesic is from about 10 μg to about 1000 μg perday.
 6. The method of claim 1 wherein said first time is from about 1 toabout 3 days, said second time is from about 1 to about 3 days, saidthird time is from about 1 to about 8 days and the sum of said first,second and third times is from about 3 to about 14 days.